Each color consists of one or more three primary colors—red, blue and green. In other words, each pixel of a digital image presents one of these three primary colors or a combination of them. Thus, a digital image can be constructed colorfully as long as each pixel of the digital image is finely defined.
There is another image formation method which presents colors by using component signals. The component signals are defined by a combination of an illumination parameter Y, a chrominance parameter Pb and a chrominance parameter Pr.
Actually, Y, Pb and Pr are a kind of linear combination of the primary colors, i.e. red, blue and green. Therefore, the primary colors RGB can be axes in a color coordinate system; for example, R-Y and B-Y can be two axes in the color coordinate system. If a color signal is transmitted by a combination of the primary colors, it needs three elements. However, if the color signal is transmitted by the color coordinate system, only two parameters are needed.
Because it is impossible to convert two chrominance parameters Pb and Pr from analog signals, a color deviation occurs and the pixels cannot show the original colors. For example, sometimes black appears as dark purple after being transmitted.
To solve this problem, a method and an apparatus for calibrating a color image transmitted by component signals are required.